In generations past, cocktails were recommended for nervous, expectant mothers. And some urged pregnant women to avoid excitement, and spend most of their time in bed.

And there seems to have been little agreement about how much exercise — if any — pregnant women should get.

Now, the advice couldn’t be more different. Researchers have learned more precisely what risks pregnant women face, and what they can do to protect their health — and the health of their unborn children. New research is increasingly revealing the dimensions of pregnant women’s vulnerability, its time frame, and long-lasting consequences.

But while there are many things expectant mothers should do, one thing they shouldn’t do is stress about what they can’t control.

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“It’s not about living in fear, it’s about living life to its fullest,” said Dr. Hope A. Ricciotti, chairwoman of Obstetrics and Gynecology at Beth Israel Deaconess Medical Center.

Pregnancy is also an opportunity for the mother to pick up good habits, Ricciotti said, and to lay a strong foundation for her child’s future health.

“It’s a jumping off point for exercise and dietary changes that can then stick for life,” Ricciotti said.

Today obesity is one of the biggest pregnancy dangers, Ricciotti and others said. Two-thirds of women are now overweight or obese — putting them at higher risk for pregnancy complications.

“This is by far our number one problem,” said Raul Artal, professor and chairman of the department of Obstetrics and Gynecology and Women’s Health at the Saint Louis University School of Medicine.

Women who are overweight or obese – particularly if they don’t get much exercise – are more likely to deliver prematurely and develop blood clots, diabetes, and heart disease later in life, among other problems. Although weight loss before pregnancy is best, moderate exercise five times a week for 30 minutes each time is enough to significantly reduce the risks during pregnancy. “You don’t have to run marathons or climb [Mount] Everest,” Artal said. “Just walking alone is beneficial.”

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In recent years, it’s become clear that excess pounds and lack of exercise also affect the child, putting him or her at higher risk for obesity, diabetes, and heart disease decades later, Artal said. Some research has suggested that genes turned on or off during pregnancy can stay that way through at least one or two generations.

Other risks to mother and child during pregnancy relate to the mother’s health status, and the environment she and her baby are exposed to, researchers said.

Mothers with uncontrolled autoimmune disease – such as rheumatoid arthritis, lupus, or Crohn’s disease – are much more vulnerable to preeclampsia, a form of pregnancy-related high blood pressure, which can put both the mother and child’s life at risk, said Dr. Sarosh Rana, an assistant professor and preeclampsia expert at Harvard Medical School and Beth Israel Deaconess Medical Center. Women with preeclampsia during pregnancy have a much higher risk of developing heart disease as they age, Rana said.

Some pregnant women should consider taking a daily baby aspirin after their first trimester if they’re at increased risk of developing preeclampsia, according to a proposed recommendation issued last week by the US Preventive Services Task Force, a government-sponsored panel of prevention experts.

Other medical groups including the American College of Obstetricians and Gynecologists and the American Heart Association also recommend low-dose aspirin therapy in high-risk pregnant women. Preeclampsia affects about 5 percent of pregnant women and can result in preterm delivery, severe hypertension, stroke, and seizures — even death of the mother in rare cases.

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“Only a small percentage of pregnant women are at high risk for preeclampsia,” Task Force chairman Dr. Michael L. LeFevre said in a statement. “Before taking aspirin, pregnant women should talk to their doctor or nurse to determine their risk and discuss if taking aspirin is right for them.”

When a mother is depressed during pregnancy, she might not be able to take care of herself as well as she’d like, putting the baby at some risk. But antidepressants can also pose problems, said Adam Urato, a maternal-fetal medicine physician at Tufts Medical Center and an assistant professor at the Tufts University School of Medicine. Women taking antidepressants are at increased risk of delivering prematurely, with some studies showing that as many as one-quarter to one-third of women taking antidepressants deliver prematurely, according to an analysis Urato published last month in the journal PLOS ONE.

For many women, non-drug approaches such as psychotherapy, are as good or better than medications, said Urato, who suggests that women consider tapering off their antidepressants before getting pregnant, unless they are likely to become severely depressed and unable to care for themselves and their child.

Frequent hand-washing can cut down on illness, but if a pregnant mom has older children at home — going to day care or school — it’s nearly impossible to avoid all illnesses during pregnancy, said Stanley Gall, a professor of obstetrics and gynecology at the University of Louisville School of Medicine.

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Gall strongly recommends that pregnant women get vaccinated before or early in their pregnancy against the flu, hepatitis A and B, pneumonia and the combination shot for diphtheria, tetanus and pertussis. All have been shown safe during pregnancy, he said, and all provide protection against diseases that could have terrible ramifications on the child.

Even the simple flu during pregnancy increases a baby’s risk four- or five-fold of developing psychiatric illnesses such as schizophrenia later in life, he said.

Pregnant women who get high fevers should always take fever-reducing medication and take care not to get dehydrated he said. Research in recent years has shown that children of women who spike a high fever in pregnancy are more likely to develop autism, among other conditions, said Irva Hertz-Picciotto, professor and chief of the division of Environmental and Occupational Health at the University of California Davis.

A study published late last month in the New England Journal of Medicine found that autism most likely begins in early pregnancy, when the child’s brain is developing. Hertz-Picciotto has shown that prenatal vitamins taken just before pregnancy, along with spacing pregnancies out by at least a year, can help reduce the likelihood that a child will develop autism.

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In today’s world, it’s nearly impossible for pregnant women – or anyone else – to avoid exposure to potentially dangerous chemicals, said R. Thomas Zoeller, an endocrinologist and professor of biology at the University of Massachusetts Amherst.

There are some chemicals “for which there’s good evidence there’s a risk,” Zoeller said, so pregnant women should try to avoid them. He includes bisphenol A, a chemical found in plastics and the lining of some food cans; phlalates, often found in beauty products; and flame retardants. He recommends against putting plastic containers – particularly baby bottles – in the dishwasher or microwave, which can allow chemicals to leach out.

But pregnant women, he said, shouldn’t make themselves crazy trying to ferret out every potential danger.

“You do the best you can do, but you still need to pursue happiness,” Zoeller said. “It doesn’t advance your ability to be a good parent to be nervous about these kind of things. There are certain things we know about. You can deal with those and move on.”